GB2188422A

GB2188422A - Method and apparatus for evaluating the slippage of a mechanical seal

Info

Publication number: GB2188422A
Application number: GB08704700A
Authority: GB
Inventors: Tadashi Kataoka
Original assignee: Agency of Industrial Science and Technology
Current assignee: National Institute of Advanced Industrial Science and Technology AIST
Priority date: 1986-03-28
Filing date: 1987-02-27
Publication date: 1987-09-30
Anticipated expiration: 2007-02-27
Also published as: US4748850A; FR2596510B1; GB8704700D0; DE3707524A1; DE3707524C2; GB2188422B; CA1292314C; FR2596510A1; JPH0460543B2; JPS62226033A

Description

GB2188422A 1 SPECIFICATION hand, the frequencies of the vibration which is

caused by the mechanical seal fall within the Method and apparatus for evaluating the high frequency band of 100 kHz to 2 MHz.

slippage of a mechanical seal The invention uses either a high frequency 70 vibration sensor having a frequency sensitivity FIELD OF THE INVENTION in the wide band of 100 kHz to 2 MHz, or a

The present invention relates to a mechani- high frequency vibration sensor having a fre cal seal and, more particularly, to method and quency sensitivity in the narrow band and hav apparatus for judging the slippage of a me- ing a resonant point within the range of 100 chanical seal. 75 kHz to 2MHz. Therefore, the effect of the noise, excluding the noise which is negligible DESCRIPTION OF THE RELATED BACK- levels. The high frequency vibration which is

GROUND ART caused by the mechanical seal can be abso Mechanical seals are often used in the shaft lutely detected by an extremely simple method sealing apparatus of rotary machines to con- 80 whereby this high frequency vibration sensor vey fluids. However, despite the fact that meis attached to the casing of the machine.

chanical seals have an extremely high probabil- In the slippage of the mechanical seal, two ity of failure compared with other mechanical contradictory functions are performed: one elements, the occurrence of the abnormal con- function seals the fluid, the other function pre dition cannot be detected until leakage actually 85 vents the abrasion of the material subject to occurs. Failure is difficult to predict. slippage by the lubricating effect of the fluid.

Hitherto, there has been proposed a method The life of a mechanical seal and the occur whereby a high frequency vibration sensor is rence of failures are largely influenced by the attached to the member subject to slippage condition and stability of the lubricating film.

(on the fixed side) of the rotary machine and 90 The high frequency vibration which is caused the high frequency vibration which is gener- by the mechanical seal occurs due to the solid ated by the slippage is detected, thereby de- contact of the materials subject to slippage tecting the abnormal condition of the member and is closely related to the condition of the subject to slippage (Japanese Patent Disclo- lubricating film. As the lubricating film ap- sure No. 55-98353). However, according to 95 proaches the dry frictional state in which the this method, the occurrence of an abnormal lubricating film is broken, the amplitude of vi condition is simply detected by comparing the bration increases and the vibration frequency magnitude of the amplitude of the detected also becomes high. In addition, the slippage of waveform. Therefore, for example, this the mechanical seal is not always constant. If method is effective to distinguish between the 100 the condition of the lubricating film is unsta- state of contact or non-contact between e.g. ble, the high frequency vibration which is the balance disk and the balance shaft, or be- caused by the mechanical seal fluctuates in tween the labyrinth seal and the shaft, and the accordance with its stability.

like. However, it is impossible to check and According to the invention, the vibration of evaluate the state of constant contact and 105 extremely high frequencies which is generated slippage such as in a mechanical seal. by the mechanical seal is measured on the There has also been proposed a method outside. One or more of the effective value of whereby the vibration of the mechanical seal the output of the high frequency vibration sen is measured by a vibration sensor having sen- sor, the energy value, and the number of sitivity in the relatively low frequency band, 110 times that the amplitude of this output ex and thereby evaluating the slippage of the me- ceeds a predetermined threshold value for a chanical seal. However, according to this unit of time are continuously measured. The method, the vibration sensor is easily influmagnitude of level of the value and the magni enced by the noise of the bearings, fluid tude of fluctuation width for the unit of time, sounds, and other sources of noise, other 115 and the number of times that the amplitude of than the mechanical seal, so that the slippage output of the high frequency vibration sensor of the mechanical seal cannot be sufficiently exceeds the predetermined threshold value for evaluated. the unit of time is measured by changing the threshold value, thereby obtaining and using SUMMARY OF THE INVENTION 120 an amplitude or similar distribution. Therefore,

It is an object of the present invention to the condition and stability of the foregoing lu provide an apparatus which can more easily bricating film can be clearly evaluated.

and reliably evaluate the slippage of a me- A specific embodiment of the present inven chanical seal in the operating mode and pre- tion will now be described in detail by way of dict failure of the mechanical seal. 125 example with reference to the accompanying The frequencies of the noise generated by drawings.

sources other than the mechanical seal e.g.

noise generated by the bearings, fluid sounds, BRIEF DESCRIPTION OF THE DRAWINGS and other sources, fall within the low fre- Figure 1 is a vertical sectional view of an quency band below 100 kHZ. On the other 130apparatus of the present invention; 2 GB2188422A 2 Figure 2 is a control block diagram; frequency sensitivity of the wide band type Figures 3 and 4 are graphs showing the sensor 14. Fig. 4 is a graph showing an sensitivity of a high frequency vibration sen- example of the frequency sensitivity of the re sor; sonant type sensor 14.

Figure 5 is a flowchart explaining the oper- 70 The microcomputer 16 reads out the detec ation of an apparatus according to the inven- tion output of the sensor 14 and converts it tion; and into a digital signal by a high speed A/D con Figures 6 and 7 are evaluation diagrams verter, thereby performing various kinds of showing the slippage of a mechanical seal. arithmetic operations and evaluations on the 75 basis of the digital signals. The calculations of DETAILED DESCRIPTION OF THE ILLUS- the effective and other values need not be

TRATED EMBODIMENT executed by the microcomputer 16. It is also An embodiment of the present invention will possible to use a method whereby the output be described below with reference to the ac- of the sensor 14 is supplied to an effective companying drawings. Fig. 1 is a vertical sec80 value voltmeter or similar apparatus, and its tional view of a pump. output is read by the microcomputer 16.

A pump haft 3 coupled to the shaft of a An example of the operation of the appara motor 1 by a shaft coupling 2 is supported by tus according to the invention will be de bearings 5 enclosed in a pump casing 4. The scribed with reference to the flowchart of Fig.

pump shaft 3 is sealed by a mechanical seal 85 5.

and a shaft sealing apparatus 6 such as an oil When the motor 1 is operated, the pump seal (not shown) and projected into a pump shaft 3 rotates through the shaft coupling 2 chamber 7. An impeller 8 is attached to one and the fluid is sucked in by the impeller 8 end portion of the pump shaft 3 in the pump and its pressure and flow speed are in chamber 7. 90 creased. Thereafter, the fluid is emitted at a The mechanical seal is constituted by: a fol- high pressure and speed. The rotary ring 12 lower ring 11 which is sealed in the pump and follower ring 11 slip relative to each casing 4 by a seal ring 9 and is movable in other. The natural vibration which is generated the axial direction; a rotary ring 12, fixed to by the slippage of the rotary ring 12 and fol- the pump shaft 3, which slips on the follower 95 lower ring 11 is transmitted by the casing 4 ring 11; and a spring 13 which is arranged without being substantially attenuated and is between the follower ring 11 and the pump detected by the sensor 14.

casing 4 and presses the follower ring 11 to- When the system starts operating, in step ward the rotary ring 12 in the axial direction. 101, the high frequency vibration which is Those components constituting the mechanical 100 generated from the slippage surfaces of the seal are substantially positioned in the fluid rings 12 and 11 is measured by the sensor which serves to both cool and lubricate the 14 and amplified by the amplifier 15. In step components. A stop means (not shown) may 102, the amplified signal is input to the micro also be provided in order to prevent the fol- computer 16 and A/D converted, one of the lower ring 11 from rotating. A high frequency 105 effective value, the energy value, and the vibration sensor 14 is attached to the pump number of times that the amplitude of the out casing 4. put exceeds a predetermined threshold va-lue Fig. 2 is a block diagram. The vibration wa- over a unit of time is obtained and sequenti veform of the mechanical seal which is de- ally stored. In step 103, a check is made to tected by the sensor 14 attached to the pump 110 determine whether the time required for the casing 4 is amplified by an amplifier 15 and above calculations has elapsed a predeter input to a microcomputer 16 for measurement mined time. The operations in steps 101 to and to be arithmetically operated. The result 103 are repeated until the foregoing predeter of the arithmetic operation is fed to an output mined time elapses. The data obtained are display apparatus 17 and displayed. 115 statistically analyzed in step 104. In step 105, In order to reduce the effect of the noises the results of the evaluation of the data and which are generated by the bearings, fluid the slippage of the mechanical seal are output sound, and other sources, other than by the to the output display apparatus 17 and dis mechanical seal, it should be noted that the played by, for example, display, printer or frequencies of these noises fall within a rela- 120 plotter. The operations in steps 101 to 105 tively low frequency band below 100 kHz. are repeated.

Thus either of the following types of high fre- Fig. 6 shows an example of an analysis of quency vibration sensors 14 is used: a wide the data of the high frequency vibration and band type sensor having frequency sensitivity an example of a method of evaluating the slip in the wide band of 100 kHz to 2 MHz; or a 125 page surfaces of the mechanical seal on the resonant type sensor having frequency sensi- - basis of the analyzed data. Fig. 6 shows the tivity in the narrow band and a resonant point frequency distribution of data which were con within the frequency range of -100 kHz to 2 tinuously measured for a fixed period of time.

MHz. In Fig. 6, the axis of abscissas denotes one of Fig. 3 is a graph showing an example of the 130 the effective value of the high frequency vibra- 3 GB2188422A 3 tion, the energy value, and the number of amplitude of the output exceeds a predeter times that the amplitude of the output ex- mined threshold value for a unit of time can ceeds a predetermined threshold value for a be continuously measured. The magnitude of unit of time, and the axis of ordinates repre- level of the values and the magnitude of the sents the frequency of the data. In the graph, 70 variation width in the unit of time, and the the broken line represents the case where number of times that the amplitude of the out good lubricating films are formed on the slip- put of the high frequency vibration sensor ex page surfaces, the solid line represents the ceeds the predetermined threshold value for case where the lubricating films are unstably the unit of time can be measured by changing formed, and the dot-dash line denotes the 75 the threshold value, thereby obtaining an am case where the lubricating films are insuffici- plitude or similar distribution. The resultant ently formed and the slippage surfaces are amplitude or similar distribution is used. As a close to the dry frictional state. The average result, the condition and stability of the lubri values and deviations in each of the above cating film of the slippage surfaces of the me cases are indicated by a, to a, and s, to s, 80 chanical seal can be evaluated.

respectively, in Fig. 6. The states of the slip- With this invention, the slippage of the me page surfaces are quantitatively evaluated and chanical seal in the operating mode can be displayed on the basis of those values. evaluated, so that failure of the mechanical Fig. 7 shows another evaluating method. seal can be predicted.

Fig. 7 shows the amplitude distribution which 85 The present invention is not limited to the is derived by counting the number of times foregoing embodiment, and other modifica that the amplitude of the output of the high tions and variations are possible within the frequency vibration sensor exceeds a predeter- spirit and scope of the appended claims of mined threshold value for a unit of time by the invention.

changing the threshold value. In Fig. 7, A indi-

Claims

cates the case where good lubricating films CLAIMS are formed on the

slippage surfaces, 0 repre- 1. An apparatus for evaluating the slippage sents the case where the lubricating films are of a mechanical seal comprising:

unstably formed, and 0 denotes the case a high frequency vibration sensor, attached where the lubricating films are insufficiently 95 to the outside of the mechanical seal of a formed and the slippage surfaces are close to rotary machine equipped with the mechanical the dry frictional state. Even by this evaluation seal, for measuring a high frequency vibration method, the states of the slippage surfaces which is generated by the mechanical seal in can be also clearly distinguished. the operating mode, and According to the present invention, an 100 arithmetic operating means for receiving the apparatus for evaluating the slippage of a me- output of said sensor, for analyzing the high chanical seal comprises: a high frequency vi frequency vibration which is generated by the bration sensor, attached to the outside of the mechanical seal in each state of the slippage mechanical seal of a rotary machine equipped surfaces of the mechanical seal, and for out- with the mechanical seal, for measuring the 105 putting evaluation values of the slippage of the high frequency vibration which is generated by mechanical seal.

the mechanical seal in the operating mode;
2. An apparatus according to claim 1, and a microcomputer for receiving the output wherein the frequency sensitivity of said high of the sensor, for analyzing the high frequency frequency vibration sensor is set to a wide vibration which is generated by the mechanical 110 band type of 100 kHz to 2 MHz or to a seal in each state of the slippage surfaces of narrow band type having a resonant point the mechanical seal, and for outputting the within a range of 100 kHz to 2 MHz, and evaluation values of the slippage of the mewherein further the frequency sensitivity below chanical seal. Therefore, the states of the slip- 100 kHz is cut by use of a high pass filter as page surfaces of the mechanical state can be 115 necessary, thereby essentially detecting high detected at any time from the beginning of frequency vibration above 100 kHz.

the use of the mechanical seal until it cannot
3. An apparatus according to claim 1 or 2, no longer be used because of abrasion. wherein said arithmetic operating means con According to the invention, since the sensor tinuously calculates one of the effective value is attached to the outside of the casing of the 120 of the output of said high frequency vibration machine, the high frequency vibration which is sensor, the energy value, and the number of generated by the mechanical seal can be ab- times that the amplitude of said output ex solutely detected by an extremely simple ceeds a predetermined threshold value for a method. unit of time, and wherein said arithmetic oper- According to the invention, the vibration of 125 ating means arithmetically operates the magni extremely high frequencies which is generated tude of the level of said value and the magni by the mechanical seal is measured. One or tude of the variation width in the unit of time.

more of the effective value of the output of
4. An apparatus according to claim 1 or 2, the high frequency vibration sensor, the en- wherein said arithmetic operating means ergy value, and the number of times that the 130 counts the number of times that the amplitude 4 GB2188422A 4 of the output of said high frequency vibration sensor exceeds a predetermine threshold value for a unit of time by changing said threshold value, thereby obtaining an amplitude distribu5 tion.
5. A method of evaluating the slippage of a mechanical seal comprising detecting the high frequency vibration which is generated by the mechanical seal and analyzing the high fre- quency vibration so detected by continuously calculating one of the effective value of the high frequency vibration, the energy value of the high frequency vibration, the energy value of the high frequency vibration and the num- ber of times that the amplitude of the high frequency vibration exceeds a predetermined threshold value for a unit of time.
6. An apparatus for evaluating the slippage of a mechanical seal substantially as hereinbe- fore described with reference to the accompanying drawings.
7. A method for evaluating the slippage of a mechanical seal substantially as hereinbefore described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd. Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A IlAY, from which copies may be obtained.

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